1. Field of the Invention
The present invention relates to the field of VSC-HVDC, and particularly to a drive signal modulation method of a modular multilevel converter and a fault isolation method.
2. Description of Related Art
The emergence of a modular multilevel converter (MMC) enables successful application of a multilevel converter in the field of VSC-HVDC. The converter of the MMC adopts a modular design and is composed of several basic unit modules having an identical structure in series, each of the modules being referred to as a converter module unit. By increasing the number of series modules and a current level in the converter, the converter can be applied to those occasions at different voltage and power levels.
However, a traditional half-bridge module unit has an inherent defect in which a direct current (DC) fault cannot be effectively handled, and a full-bridge module capable of suppressing a DC fault current also has problems such as large losses and high costs. Thus, how to optimize the performance of the MMC becomes a key technical factor for solving the problems in DC interconnection.
In view of this, the present inventors have conducted investigations and improvements on a drive signal modulation method of a modular multilevel converter, resulting in the present application.